Fibers, nonwoven fabrics and absorbent articles comprising a biodegradable polyhydroxyalkanoate comprising 3-hydroxybutyrate and 3-hydroxyhexanoate

ABSTRACT

The present invention relates to fibers, and nonwovens comprising said fibers, comprising a biodegradable copolymer, wherein the copolymer comprises at least two randomly repeating monomer units (RRMU) wherein the first RRMU monomer unit has the structure ##STR1## and the second RRMU has the structure ##STR2## wherein at least 50% of the RRMUs have the structure of the first RRMU. The present invention further relates to an absorbent article comprising a liquid pervious topsheet, a biodegradable liquid impervious backsheet comprising the above fibers and/or nonwovens, and an absorbent core positioned between the topsheet and the backsheet.

This application is a divisional of U.S. application Ser. No.08/593,027, filed Jan. 29, 1996, now U.S. Pat. No. 6,013,590, which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to biodegradable copolymers; fibers, andnonwoven fabrics comprising the copolymers; and disposable absorbentarticles such as diapers, sanitary napkins and pantiliners, comprisingsuch fibers, and nonwoven fabrics.

BACKGROUND

A wide variety of absorbent articles designed to be efficient for theabsorption of body fluids such as blood, urine, menses, and the like,are known. Disposable products of this type generally comprise some sortof fluid-permeable topsheet material, an absorbent core, and afluid-impermeable backsheet material. Heretofore, such absorbentstructures have been prepared using, for example, topsheet materialsprepared from woven, nonwoven, or porous formed-film polyethylene orpolypropylene materials. Backsheet materials typically comprise flexiblepolyethylene sheets. Absorbent core materials typically comprise woodpulp fibers or wood pulp fibers in combination with absorbent gellingmaterials. One aspect of such absorbent articles that has recently beenconsidered is their disposability. Although such products largelycomprise materials which would be expected ultimately to degrade, andalthough products of this type contribute only a very small percentageof the total solid waste materials generated by consumers each year,nevertheless, there is currently a perceived need to devise suchdisposable products from materials which are compostable.

A conventional disposable absorbent product is already to a large extentcompostable. A typical disposable diaper, for example, consists of about80% of compostable materials, e.g., wood pulp fibers, and the like. Inthe composting process soiled disposable absorbent articles are shreddedand commingled with organic waste prior to the composting per se. Aftercomposting is complete, the non-compostable particles are screened out.In this manner even today's absorbent articles can successfully beprocessed in commercial composting plants.

Nevertheless, there is a need for reducing the amount of non-compostablematerials in disposable absorbent articles. There is a particular needto replace polyethylene backsheets and nonwoven fabrics in absorbentarticles with liquid impervious films or nonwovens of compostablematerial, because the backsheet is typically one of the largestnon-compostable components of a conventional disposable absorbentarticle.

In addition to being compostable, the films and nonwovens employed asbacksheets for absorbent articles must satisfy many other performancerequirements. For example, the resins should be thermoplastic such thatconventional film or nonwoven processing methods can be employed. Thesemethods include cast film and blown film extrusion of single layerstructures and cast, blown film coextrusion of multilayer structures, orweb-making by carding, air-laying, wet-forming, spinbonding, andmeltblowing. Other methods include extrusion coating of one material onone or both sides of a compostable substrate such as another film, anonwoven fabric, or a paper web.

Still other properties are essential in product converting operationswhere the films, fibers, and nonwovens are used to fabricate absorbentarticles. Properties such as tensile strength, tensile modulus, tearstrength, and thermal softening point determine to a large extent howwell, for example, a film will run on converting lines.

In addition to the aforementioned properties, still other properties areneeded to meet the end user requirements of the absorbent article. Forexample, film properties such as impact strength, puncture strength, andmoisture transmission are important since they influence the absorbentarticle's durability and containment while being worn.

Once the absorbent article is disposed of and enters a compostingprocess, other properties become important. Regardless of whetherincoming waste is preshredded or not, it is important that the film,fiber, or large film or nonwoven fragments undergo an initial breakup tomuch smaller particles during the initial stages of composting.Otherwise, the films, fibers, or large fragments may be screened out ofthe compost stream and may never become part of the final compost.

In the past, the biodegradability and physical properties of a varietyof polyhydroxyalkanoates have been studied. Polyhydroxyalkanoates arepolyester compounds produced by a variety of microorganisms, such asbacteria and algae. While polyhydroxyalkanoates have been of generalinterest because of their biodegradable nature, their actual use as aplastic material has been hampered by their thermal instability. Forexample, poly-3-hydroxybutyrate (PHB) is a natural energy-storageproduct of bacteria and algae, and is present in discrete granuleswithin the cell cytoplasm. However, unlike other biologicallysynthesized polymers such as proteins and polysaccharides, PHB isthermoplastic having a high degree of crystallinity and a well-definedmelt temperature of about 180° C. Unfortunately, PHB becomes unstableand degrades at elevated temperatures near its melt temperature. Due tothis thermal instability, commercial applications of PHB have beenextremely limited.

As a result, investigators have studied other polyhydroxyalkanoates suchas poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), in the hopes ofdiscovering a polyhydroxyalkanoate having sufficient thermal stabilityand other suitable chemical and physical properties for use in practicalapplications. Unfortunately, polyhydroxyalkanoates such as PHB and PHBVare difficult to process into films, fibers, and nonwovens suitable forbacksheet applications. As previously discussed, the thermal instabilityof PHB makes such processing nearly impossible. Furthermore, the slowcrystallization rates and flow properties of PHB and PHBV make film,fiber, and nonwoven processing difficult. Examples of PHB homopolymerand PHBV copolymers are described in U.S. Pat. 4,393,167, Holmes et al.,issued Jul. 12, 1983, and U.S. Pat. No. 4,880,592, issued Nov. 14, 1989.PHBV copolymers are commercially available from Imperial ChemicalIndustries under the tradename BIOPOL. PHBV copolymers are currentlyproduced with valerate contents ranging from about 5 to about 24 mol %.Increasing valerate content decreases the melt temperature,crystallinity, and stiffness of the polymer. An overview of BIOPOLtechnology is provided in BUSINESS 2000+ (Winter, 1990).

Due to the slow crystallization rate, a film, fiber, or nonwoven madefrom PHBV will stick to itself even after cooling; a substantialfraction of the PHBV remains amorphous and tacky for long periods oftime. In cast film operations, where the film is immediately cooled onchill rolls after leaving the film die, molten PHBV often sticks to therolls restricting the speed at which the film can be processed, or evenpreventing the film from being collected. In blown films, residual tackof the PHBV causes the tubular film to stick to itself after it has beencooled and collapsed for winding. In spun fibers, the fiber bundle willlikewise stick and collapse.

U.S. Pat. No. 4,880,592, Martini et al., issued Nov. 14, 1989, disclosesa means of achieving a PHBV monolayer film for diaper backsheetapplications by coextruding the PHBV between two layers of sacrificialpolymer, for example a polyolefin, stretching and orienting themultilayer film, and then stripping away the polyolefin layers after thePHBV has had time to crystallize. The remaining PHBV film is thenlaminated to either water soluble films or water insoluble films such aspolyvinylidene chloride or other polyolefins. Unfortunately, suchdrastic and cumbersome processing measures are necessary in an attemptto avoid the inherent difficulties associated with processing PHBV intofilms.

Based on the foregoing, there is a need for disposable absorbentarticles (e.g., diapers) with increased biodegradability. To satisfythis need, there is a preliminary need for a biodegradable copolymerwhich is capable of being easily processed into a film, fiber, ornonwoven for use in such disposable sanitary garments.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a film comprising abiodegradable polyhydroxyalkanoate.

It is also an object of the present invention to provide a fibercomprising a biodegradable PHA.

It is also an object of the present invention to provide a nonwovencomprising a biodegradable PHA.

It is also an object of the present invention to provide a disposablesanitary garment comprising a film, fiber, or nonwoven comprising abiodegradable PHA.

SUMMARY

The present invention relates to a film, fiber, or nonwoven comprising abiodegradable copolymer, wherein the copolymer comprises at least tworandomly repeating monomer units (RRMU) wherein the first RRMU has thestructure ##STR3## and the second RRMU has the structure ##STR4##wherein at least 50% of the RRMUs have the structure of the first RRMU.

The present invention further relates to an absorbent article comprisinga liquid pervious topsheet, a biodegradable liquid impervious backsheetcomprising the above film or nonwoven, and an absorbent core positionedbetween the topsheet and the backsheet.

DETAILED DESCRIPTION

The present invention answers the need for a biodegradable copolymerwhich is capable of being easily processed into a film, fiber, ornonwoven. The present invention further answers the need for disposableabsorbent articles with increased biodegradability.

As used herein, "ASTM" means American Society for Testing and Materials.

As used herein, "comprising" means that other steps and otheringredients which do not affect the end result can be added. This termencompasses the terms "consisting of" and "consisting essentially of".

As used herein, "alkyl" means a saturated carbon-containing chain whichmay be straight or branched; and substituted (mono- or poly-) orunsubstituted.

As used herein, "alkenyl" means a carbon-containing chain which may bemonounsaturated (i.e., one double bond in the chain) or polyunsaturated(i.e., two or more double bonds in the chain); straight or branched; andsubstituted (mono- or poly-) or unsubstituted.

As used herein, "PHA" means a polyhydroxyalkanoate of the presentinvention.

As used herein, "PHB" means the homopolymer poly(3-hydroxybutyrate).

As used herein, "PHB-Hx" means the copolymerpoly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

As used herein, "PHBV" means the copolymerpoly(3-hydroxybutyrate-co-3-hydroxyvalerate).

As used herein, "biodegradable" means the ability of a compound toultimately be degraded completely into CO₂ and water or biomass bymicroorganisms and/or natural environmental factors.

As used herein, "compostable" means a material that meets the followingthree requirements: (1) the material is capable of being processed in acomposting facility for solid waste; (2) if so processed, the materialwill end up in the final compost; and (3) if the compost is used in thesoil, the material will ultimately biodegrade in the soil.

For example, a polymer film material present in solid waste submitted toa composting facility for processing does not necessarily end up in thefinal compost. Certain composting facilities subject the solid wastestream to air classification prior to further processing, in order toseparate paper and other materials. A polymer film would most probablybe separated from the solid waste stream in such an air classificationand therefore not be processed in the composting facility. Nevertheless,it may still be a "compostable" material according to the abovedefinition because it is "capable" of being processed in a compostingfacility.

The requirement that the material ends up in the final compost typicallymeans that it undergoes a form of degradation in the composting process.Typically, the solid waste stream will be subjected to a shredding stepin an early phase of the composting process. As a result, the polymerfilm will be present as shreds rather than a sheet. In the final phaseof the composting process, the finished compost will be subjected to ascreening step. Typically, the polymer shreds will not pass through thescreens if they have retained the size they had immediately after theshredding step. The compostable materials of the present invention willhave lost enough of their integrity during the composting process toallow partially degraded shreds to pass through the screens. However, itis conceivable that a composting facility might subject the solid wastestream to a very rigorous shredding and a rather coarse screening, inwhich case nondegradable polymers like polyethylene would meetrequirement (2). Therefore, meeting requirement (2) is not enough for amaterial to be compostable within the present definition.

What distinguishes the compostable material as defined herein frommaterial like polyethylene is requirement (3), that the materialultimately biodegrade in the soil. This biodegradability requirement isnot essential to the composting process or the use of composting soil.Solid waste and the compost resulting therefrom may contain all kinds ofnonbiodegradable materials, for example, sand. However, to avoid a buildup of man-made materials in the soil, it is required herein that suchmaterials be fully biodegradable. By the same token, it is not at allnecessary that this biodegradation be fast. As long as the materialitself and intermediate decomposition products are not toxic orotherwise harmful to the soil or crops, it is fully acceptable thattheir biodegradation takes several months or even years, since thisrequirement is present only to avoid an accumulation of man-madematerials in the soil.

All copolymer composition ratios recited herein refer to mole ratios,unless specifically indicated otherwise.

A. Films

The present invention relates to biodegradable copolymers which aresurprisingly easy to process into films as compared to the homopolymerPHB and copolymer PHBV. Prior to Applicants' invention,polyhydroxyalkanoates studied for use in commercial plastics productionpresented significant impediments to their use in plastics. As discussedabove, polyhydroxyalkanoates such as PHB and the copolymer PHBV aredifficult to process due to their thermal instability. Furthermore, suchpolyhydroxyalkanoates were especially difficult to process into filmsdue to their slow crystallization rate. Applicants have found that PHAcopolymers of the present invention, which comprise a second RRMU asdefined above having an alkyl branch of at least three (3) carbons, aresurprisingly easier to process into films, especially as compared to PHBor PHBV. Applicants surprisingly discovered, such linear, randomcopolymers with a limited number of medium sized (e.g., C₃ -C₁₉)branches provide, in addition to biodegradability, the followingproperties, particularly as compared to PHB or PHBV: a) a lower melttemperature, b) a lower degree of crystallinity, and c) an improved meltrheology.

Without being bound by theory, Applicants believe characteristics a) andb) are achieved by exclusion of the second RRMU from the crystal latticeof the first RRMU, thereby resulting in a decreased temperature forthermal processing and improved stiffness and elongation properties.Again, without being bound by theory, Applicants believe characteristicc) is achieved by increased entanglement between the copolymer chainsdue to the side chains of the second RRMU. Such increased entanglementmay occur by increased hydrodynamic volume of the copolymer (e.g., thesecond monomer unit creates kinks in the helical structure), the"hooking" or "catching" of the side chains on different copolymerbackbones while in the melt, or the decreased chain scission due to thelower Tm (i.e., the enlarged thermal process window).

Biodegradable PHAs useful for processing into the films of the presentinvention comprises at least two randomly repeating monomer units (RRMU)wherein the first RRMU has the structure ##STR5## and the second RRMUhas the structure ##STR6## wherein at least 50% of the RRMUs have thestructure of the first RRMU.

In a preferred embodiment, the PHA comprises one or more additionalRRMUs having the structure ##STR7## wherein R¹ is H, or a C₂ or C₄, C₅,C₆, C₇, C₈, C₉, C₁₀, C₁₁, C₁₂, C₁₃, C₁₄, C₁₅, C₁₆, C₁₇, C₁₈, or C₁₉alkyl or alkenyl; and n is 1 or 2.

As used herein, "film" means an extremely thin continuous piece of asubstance having a high length to thickness ratio and a high width tothickness ratio. While there is no requirement for a precise upper limitof thickness, a preferred upper limit would be about 0.254 mm, morepreferably still 0.01 mm, more preferably still 0.005 mm. The protectivevalue of any film depends on its being continuous, i.e., without holesor cracks, since it must be an efficient barrier to molecules such asatmospheric water vapor and oxygen. In a preferred embodiment of thepresent invention, the film of the present invention is liquidimpervious and suitable for use in absorbent disposable sanitarygarments such as disposable diapers, feminine hygiene products and thelike. More preferably, films of the present invention, in addition toincreased biodegradability and/or compostability, have the followingproperties:

a) a machine direction (MD) tensile modulus from about 10,000 to about100,000 lbs./sq. in. (6.895×10⁸ dynes/sq. cm to 6.895×10⁹ dynes/sq. cm),

b) a MD tear strength of at least 70 grams per 25.4 μm of thickness,

c) a cross machine direction (CD) tear strength of at least 70 grams per25.4μ of thickness,

d) an impact strength of at least 12 cm as measured by falling balldrop,

e) a moisture transport rate less than about 0.0012 grams per squarecentimeter per 16 hours,

f) a modulus at 60° C. of at least 5.52×10⁷ dynes/sq. cm (800 lbs./sq.in), and

g) a thickness from about 12 μm to about 75 μm.

Methods for testing for such performance criteria are discussed in moredetail below.

1. Performance Criteria and Test Methods for Films

For a film to perform satisfactorily as a compostable disposable diaperbacksheet, it must be made of resins or structures that arebiodegradable and it must demonstrate the following properties of highstrength, adequate fluid barrier, appropriate modulus or flexibility,and adequately high melting point.

The backsheets of disposable diapers must have sufficient strength bothto process on a high speed disposable diaper converting machine and toprovide a "wetproof" barrier in use on an infant. It must besufficiently wetproof so that the clothing or bedding, either that ofthe infant or of the caregiver, is not wet or soiled. It must have amodulus or flexibility that is, at the same time, low enough to be asoft, pleasing material to be used as the outer covering of an infantdiaper yet high enough to handle easily on high speed disposable diaperconverters without wrinkling, folding, or creasing. It must havesufficient resistance to heat such that it will not deform, melt, orpermanently loose strength in typical hot storage conditions or looseits integrity on high speed disposable diaper converters which typicallyuse hot melt adhesives to bond the components of a disposable diapertogether.

Films that are sufficiently strong to be suitable as biodegradableand/or compostable backsheets for disposable diapers preferablydemonstrate two properties: (a) resistance to rupture from a droppedweight and (b) resistance to tearing in both the machine direction ofmanufacture and the cross-machine direction of manufacture. Preferredbacksheets of the present invention can withstand the drop of aspherical steel ball of about 19 millimeters in diameter and 27.6 to28.6 gram mass from a height of 12 centimeters so that at least 50% ofthe tests result in no rupture of any size (deformation is acceptable).Preferred materials are those that exhibit 50% or less failures from aheight of more than 20 centimeters. Similarly, acceptable backsheets ofthe present invention demonstrate an average tear propagation resistanceof 70 grams per 25.4 micron thickness of material in both the machinedirection and cross-machine direction of manufacture when a standardElmendorf pendulum-type test device, such as Elmendorf Model No. 60-100,is employed against 16 plies of material which have been prepared with acut or notch according to TAPPI Method T 414om-88. More preferable arethose backsheets that demonstrate tear propagation resistances of 200 ormore grams per 25.4 micron thickness in the cross-machine directionbecause these are particularly good at avoiding a tendency to fail inuse by splitting.

It has also been found that films of sufficient barrier to moisturetransport are those that permit less than 0.0012 grams of syntheticurine to pass into an absorbent paper towel per square centimeter ofarea per 25.4 micron thickness for every 16 hours of time when the testfilm is located between the absorbent paper towel and a typicalabsorbent gelling material-containing diaper core and a pressuresimulating that of a baby. The specific conditions of the test are thatthe area of the core is larger than that of the test material, the coreis loaded with synthetic urine to its theoretical capacity and it isunder a weight of about 35 g/cm² (0.5 psi).

It has also been found that materials of sufficient heat resistancedemonstrate a Vicat softening point of at least 45° C. Vicat softeningis tested using a Heat Distortion Apparatus Model No. CS-107 orequivalent and a modification of ASTM D-1525. The modification is in thepreparation of the sample. A 19 square millimeter size film of 4.5 to6.5 mm thickness is prepared for Vicat needle penetration tests bymelting the material to be tested into a mold using a temperature of120° C. and pressure of 7.031×10⁵ g/cm² (10,000 psi) (using a Carver orsimilar press) for two minutes after a warm-up period of at least 2minutes. The Vicat softening point is the temperature at which aflat-ended needle of 1 sq. mm circular cross section will penetrate thesample to a depth of 0.1 cm under a load 1000 g using a uniformtemperature rise rate of 50° C. per hour.

It has also been found that materials of sufficient machine directionmodulus demonstrate a 1% secant-type modulus above at least about6.895×10⁸ dynes/cm² (10,000 psi) and below about 6.895×10⁹ dynes/cm²(100,000 psi). The test is performed on an electronic tensile testmachine such as the Instron Model 4201. A 2.54 cm wide strip ofmaterial, preferably of 0.00254 cm in thickness, is cut to a length ofabout 30 cm with the longer dimension parallel to the machine directionof the material. The test strip is clamped into the jaws of the tensiletestor so that the gauge or actual length of the material tested is 25.4cm The jaws are separated at a slow speed in the range of 2.54 cm perminute to 25.4 cm per minute and a stress-strain curve is plotted on achart within an attached recording device. The 1% secant modulus isdetermined by reading the stress or tensile from the chart at the 1%elongation strain point. For example, the 1% strain point is achievedwhen the distance between jaws has increased by 0.254 cm. When the jawsare separating at the rate of 2.54 cm per minute and the recordingdevice is running at a speed of 25.4 cm per minute, the 1% strain pointwill be located at a distance of 2.54 cm from the initial point. Thetensile response is divided by the thickness of the sample material ifit is not 0.00254 cm in thickness. Particularly soft, and thereforepreferred, materials exhibit 1% secant moduli in the range of 6.895×10⁸to 2.068×10⁹ dynes/cm² (10,000 to 30,000 psi).

Since absorbent articles may experience temperatures as high as 140° F.(60° C.) during warehouse storage or shipping in trucks or railcars, itis important that the backsheet film and other components retain theirintegrity at these temperatures. Although it is expected that themodulus of the films will decrease somewhat between 20° C. and 60° C.,the modulus should not decrease too far and allow the film to deform inthe package before it reaches the end user.

For example, a polyethylene backsheet with a room temperature modulus ofabout 4×10⁹ dynes/cm² (58,000 psi) may have a 60° C. modulus of 1.2×10⁹dynes/cm² (18,560 psi) which is acceptable. A softer polyethylenebacksheet with a room temperature modulus of about 8.0×10⁸ dynes/cm²(11,600 psi) may have a 60° C. modulus of about 3.5×10⁸ dynes/cm² (5,076psi) which is still acceptable. In general, an acceptable backsheet filmof the present invention will have a 60° C. modulus of at least 5.52×10⁷dynes/cm² (800 psi).

The modulus dependence on temperature, also called a modulus/temperaturespectrum, is best measured on a dynamic mechanical analyzer (DMA) suchas a Perkin Elmer 7 Series/Unix TMA 7 Thermomechanical Analyzer equippedwith a 7 Series/Unix DMA 7 Temperature/Time software package,hereinafter referred to as the DMA 7, available from the Perkin-ElmerCorporation of Norwalk, Conn. Many other types of DMA devices exist, andthe use of dynamic mechanical analysis to study the modulus/temperaturespectra of polymers is well known to those skilled in the art of polymer(or copolymer) characterization. This information is well summarized intwo books, the first being DYNAMIC MECHANICAL ANALYSIS OF POLYMERICMATERIAL, MATERIALS SCIENCE MONOGRAPHS VOLUME 1 by T. Murayama (ElsevierPublishing Co., 1978) and the second being MECHANICAL PROPERTIES OFPOLYMERS AND COMPOSITES, VOLUME 1 by L. E. Nielsen (Marcel Dekker,1974).

The mechanism of operation and procedures for using the DMA 7 are foundin Perkin-Elmer Users' Manuals 0993-8677 and 0993-8679, both dated May,1991. To those skilled in the use of the DMA 7, the following runconditions should be sufficient to replicate the 60° C. modulus datapresented hereinafter.

To measure the modulus/temperature spectrum of a film specimen, the DMA7 is set to run in temperature scan mode and equipped with an extensionmeasuring system (EMS). A film specimen approximately 3 mm wide, 0.0254mm thick, and of sufficient length to allow 6 to 8 mm of length betweenthe specimen grips is mounted in the EMS. The apparatus is then enclosedin an environmental chamber swept continuously with helium gas. Stressis applied to the film in the length direction to achieve a deformationor strain of 0.1 percent of the original length. A dynamic sinusoidalstrain is applied to the specimen at a frequency of 5 cycles per second.In the temperature scan mode, the temperature is increased at a rate of3.0° C./minute from 25° C. to the point where the specimen melts orbreaks, while the frequency and stress are held constant.Temperature-dependent behavior is characterized by monitoring changes instrain and the phase difference in time between stress and strain.Storage modulus values in Pascals are calculated by the computer alongwith other data and displayed as functions of temperature on a videodisplay terminal. Normally the data are saved on computer disk and ahard copy of the storage modulus/temperature spectrum printed forfurther review. The 60° C. modulus is determined directly from thespectrum.

2. Method of Film Manufacture

The films of the present invention used as backsheets having increasedbiodegradability and/or compostability may be processed usingconventional procedures for producing single or multilayer films onconventional film-making equipment. Pellets of the PHAs of the presentinvention can be first dry blended and then melt mixed in a filmextruder. Alternatively, if insufficient mixing occurs in the filmextruder, the pellets can be first dry blended and then melt mixed in aprecompounding extruder followed by repelletization prior to filmextrusion.

The PHAs of the present invention can be melt processed into films usingeither cast or blown film extrusion methods both of which are describedin PLASTICS EXTRUSION TECHNOLOGY--2nd Ed., by Allan A. Griff (VanNostrand Reinhold--1976). Cast film is extruded through a linear slotdie. Generally the flat web is cooled on a large moving polished metalroll. It quickly cools, and peels off this first roll, passes over oneor more auxiliary cooling rolls, then through a set of rubber-coatedpull or "haul-off" rolls, and finally to a winder. A method of making acast backsheet film for the absorbent articles of the present inventionis described in an example below.

In blown film extrusion, the melt is extruded upward through a thinannular die opening. This process is also referred to as tubular filmextrusion. Air is introduced through the center of the die to inflatethe tube and thereby causing it to expand. A moving bubble is thusformed which is held at a constant size by control of internal airpressure. The tube of film is cooled by air, blown through one or morechill rings surrounding the tube. The tube is then collapsed by drawingit into a flattening frame through a pair of pull rolls and into awinder. For backsheet applications the flattened tubular film issubsequently slit open, unfolded, and further slit into widthsappropriate for use in products.

Both cast film and blown film processes can be used to produce eithermonolayer or multilayer film structures. For the production of monolayerfilms from a single thermoplastic material or blend of thermoplasticcomponents only a single extruder and single manifold die are required.

For the production of multilayer films of the present invention,coextrusion processes are preferably employed. Such processes requiremore than one extruder and either a coextrusion feedblock ormulti-manifold die system or combination of the two to achieve themultilayer film structure.

U.S. Pat. Nos. 4,152,387, and 4,197,069, disclose the feedblockprinciple of coextrusion. Multiple extruders are connected to thefeedblock which employs moveable flow dividers to proportionally changethe geometry of each individual flow channel in direct relation to thevolume of polymer passing through said flow channels. The flow channelsare designed such that at their point of confluence, the materials flowtogether at the same flow rate and pressure eliminating interfacialstress and flow instabilities. Once the materials are joined in thefeedblock, they flow into a single manifold die as a compositestructure. It is important in such processes that the melt viscositiesand melt temperatures of the materials do not differ too greatly;otherwise flow instabilities can result in the die leading to poorcontrol of layer thickness distribution in the multilayer film.

An alternative to feedblock coextrusion is a multi-manifold or vane dieas disclosed in aforementioned U.S. Pat. Nos. 4,152,387, 4,197,069, andin U.S. Pat. No. 4,533,308. Whereas in the feedblock system melt streamsare brought together outside and prior to entering the die body, in amulti-manifold or vane die each melt stream has its own manifold in thedie where the polymers spread independently in their respectivemanifolds. The melt streams are married near the die exit with each meltstream at full die width. Moveable vanes provide adjustability of theexit of each flow channel in direct proportion to the volume of materialflowing through it, allowing the melts to flow together at the samelinear flow rate, pressure, and desired width.

Since the melt flow properties and melt temperatures of the processedmaterials may vary widely, use of a vane die has several advantages. Thedie lends itself toward thermal isolation characteristics whereinmaterials of greatly differing melt temperatures, for example up to 175°F. (80° C.), can be processed together.

Each manifold in a vane die can be designed and tailored to a specificpolymer (or copolymer). Thus the flow of each polymer is influenced onlyby the design of its manifold, and not by forces imposed by otherpolymers. This allows materials with greatly differing melt viscositiesto be coextruded into multilayer films. In addition, the vane die alsoprovides the ability to tailor the width of individual manifolds, suchthat an internal layer, for example a water soluble biodegradablepolymer like Vinex 2034, can be completely surrounded by water insolublematerials leaving no exposed edges susceptible to water. Theaforementioned patents also disclose the combined use of feedblocksystems and vane dies to achieve more complex multilayer structures.

The multilayer films of the present invention may comprise two or morelayers. In general, balanced or symmetrical three-layer and five-layerfilms are preferred. Balanced three-layer multilayer films comprise acenter core layer and two identical outer layers, wherein said centercore layer is positioned between said two outer layers. Balancedfive-layer multilayer films comprise a center core layer, two identicaltie layers, and two identical outer layers, wherein said center corelayer is positioned between said two tie layers, and a tie layer ispositioned between said center core layer and each outer layer. Balancedfilms, though not essential to the films of the present invention, areless prone to curling or warping than unbalanced multilayer films.

In three layer films, the center core layer may comprise 30 to 80percent of the films' total thickness and each outer layer comprises 10to 35 percent of the films' total thickness. Tie layers, when employed,each comprise from about 5 percent to about 10 percent of the films'total thickness.

3. Crystallinity

The volume percent crystallinity (Φ_(C)) of a semi-crystalline polymer(or copolymer) often determines what type of end-use properties thepolymer possesses. For example, highly (greater than 50%) crystallinepolyethylene polymers are strong and stiff, and suitable for productssuch as plastic milk containers. Low crystalline polyethylene, on theother hand, is flexible and tough, and is suitable for products such asfood wraps and garbage bags. Crystallinity can be determined in a numberof ways, including x-ray diffraction, differential scanning calorimetry(DSC), density measurements, and infrared absorption. The most suitablemethod depends upon the material being tested.

X-ray diffraction is most appropriate when little is known about thethermal properties of the material and crystal structural changes mayoccur. The basic principle relies on the fact that amorphous parts ofthe material scatter x-rays in a diffuse or broad range of angles whilecrystals diffract x-rays into sharp, precisely defined angles. The totalscattered intensity is constant, however. This allows calculation of theamount of crystalline material in a sample if the amorphous andcrystalline diffracted intensities can be separated. A very precisemethod has been developed by Ruland, which can detect differences inpercent crystallinity as small as 2% (see Vonk, C., F. J. Balta-Calleja,X-RAY SCATTERING FROM SYNTHETIC POLYMERS, Elsevier: Amsterdam, (1989);and Alexander, L., X-RAY DIFFRACTION METHODS IN POLYMER SCIENCE, RobertKreiger Pub. Co., New York, (1979)).

Upon melting, crystals require a fixed amount of heat at the meltingtemperature transforming from crystalline to molten matter. This heat offusion can be measured by a number of thermal techniques, the mostpopular being DSC. If the heat of fusion of a 100% crystalline materialis known, and no significant annealing, or melt/recrystallisationphenomena occur upon heating to the melt, then DSC can quite accuratelydetermine weight fraction crystallinity (see THERMAL CHARACTERIZATION OFPOLYMER MATERIALS, E. Turi, Ed., Academic Press, New York, (1980); andWunderlich, B., MACROMOLECULAR PHYSICS, Academic Press, New York,(1980)).

If the densities of the pure crystalline and pure amorphous material isknown then density measurements of a material can yield the degree ofcrystallinity. This assumes additivity of specific volumes, but thisrequirement is fulfilled for polymers (or copolymers) of homogeneousstructure. This method depends on careful sample preparation so that nobubbles or large voids exist in the sample.

If purely crystalline and amorphous absorption bands can be identified,then the infrared absorption spectrum offers a convenient way ofdetermining crystallinity (see Tadokoro, H., STRUCTURE OF CRYSTALLINEPOLYMERS, John Wiley & Sons, New York, (1979)).

It should be noted that different techniques will often give rise toslightly different values of Φ_(C), because they are based on differentphysical principles. For example, density measurements often give highervalues than x-ray diffraction. This is due to the continuous changing ofthe density in the interface between crystalline and amorphous polymer(or copolymer) material. While x-ray diffraction does not detect thismatter as crystalline, density measurements will be affected by thisinterface region.

For purposes of processing into a film, the PHAs of the presentinvention preferably have a crystallinity of from about 2% to about 65%as measured via x-ray diffraction; more preferably from about 5% toabout 50%; more preferably still from about 20% to about 40%.

B. Fibers

Applicants have further discovered the biodegradable PHAs of the presentinvention are surprisingly easy to process into fibers. As used herein,"fiber" refers to a flexible, macroscopically homogeneous body having ahigh length-to-width ratio and a small cross section. A general overviewof fibers can be found in the ENCYCLOPEDIA OF POLYMER SCIENCE ANDENGINEERING, Vol. 6, p. 647-755 and pp. 802-839, John Wiley and Sons,New York, (1986) (hereinafter referred to as "EPSE-1"). The fibers ofthe present invention are useful as textiles in yams for garments. Forexample, the fibers can be used to form a nonwoven backsheet for anabsorbent article. Such use is particularly attractive in, e.g.,diapers, thereby providing a disposable biodegradable backsheetimparting a cloth-like feel.

The fibers of the present invention are also useful for manufacturinglightweight fibrous materials useful in agricultural applications toprotect, promote, or control plant growth. They are also used in greenhouse thermal screens, crop row covers, turf covers, weed barriers andhydroponics. Key properties are light, air, and moisture permeability.An important aspect is cost effectiveness when considered in terms ofweight, strength, and dimension stability.

An elastomeric fiber is a fiber that consists of polymers (orcopolymers) with a main glass transition temperature much below roomtemperature (see EPSE-1). This criterion excludes some fibers withelastic properties, such as crimped hard fibers, but allows inclusion ofmulti-constituent fibers where one of the constituents is an elastomer.All elastomeric fibers are characterized by a higher elongation atbreak, lower modulus, and higher recovery from large deformation thannormal fibers.

1. Methods of Fiber Manufacture

The fibers of the present invention may be processed using a variety ofconventional techniques well-known in the art including, but not limitedto, melt spinning, dry spinning, and wet spinning. Combinations of thesethree basic processes are often used.

In melt spinning the PHA of the present invention is heated above itsmelting point and the molten PHA is forced through a spinneret. Aspinneret is a die with many small orifices which are varied in number,shape and diameter (see EPSE-1). The jet of molten PHA is passed througha cooling zone where the PHA solidifies and is then transferred topost-drawing and take-up equipment.

In dry spinning, the PHA of the present invention is dissolved and thePHA solution is extruded under pressure through a spinneret (seeEPSE-1). The jet of PHA solution is passed through a heating zone wherethe solvent evaporates and the filament solidifies.

In wet spinning, the PHA of the present invention is also dissolved andthe solution is forced through a spinneret which is submerged in acoagulation bath (see ESPE-1). As the PHA solution emerges from thespinneret orifices within the coagulation bath, the PHA is eitherprecipitated or chemically regenerated. Usually, all these processesneed further drawing for useful properties to be obtained, for exampleto serve as textile fibers. "Drawing" refers to stretching andattenuation of fibers to achieve an irreversible extension, inducemolecular orientation, and develop a fiber-fine structure (see ESPE-1).This fine structure is characterized by a high degree of crystallinityand by orientation of both the crystallites and the amorphous PHA chainsegments.

C. Nonwovens

In another embodiment of the present invention, the PHA is formed into anonwoven. As used herein "nonwoven" means porous, textile likematerials, usually in flat sheet form, composed primarily, or entirely,of fibers assembled in webs that are manufactured by processes otherthan spinning, weaving, or knitting. A general overview of nonwovenfabrics can be found in the ENCYCLOPEDIA OF POLYMER SCIENCE ANDENGINEERING, Second Edition, Vol. 10, pp. 204-226 (referred to hereafteras "EPSE-2"). Other names for these materials are bonded fabrics, formedfabrics, or engineered fabrics. The thickness of the fabric sheets mayvary from 25 mm to several centimeters, and the weight from 10 g/m² to 1kg/m². Nonwoven fabrics have a wide range of physical propertiesdepending on the material and process used in forming the web. A fabricmay be self-supporting and stiff as paper or drapable as a conventionalcloth fabric.

In contrast to conventional textiles, the fundamental structure of allnonwovens is a web of fibers arranged more or less randomly (NONWOVENSIND., Vol. 17, p. 36 (March 1986), NONWOVENS WORLD, Vol. 1, p. 36(May-June 1986)). Thus, the key element is the single fiber. Tensile,tear, and tactile properties in the nonwoven arise from adhesive orother chemical and physical bonding, fiber-to-fiber friction created byentanglement, and reinforcement by other materials such as foams andfilms (see EPSE-2).

1. Method of Manufacture of Nonwoven Fabrics

The nonwoven fabrics of the present invention may be made byconventional techniques known in the art. The production of nonwovenfabrics involves: 1) making fibers of various lengths and diameters; 2)creating a web of these fibers; and 3) bonding of fibers within the webby adhesive, or mechanical-frictional forces created by fiber contact orentanglement. In addition to these steps, reinforcing the web by forminga composite with other materials (e.g., yarns, scrims, films, nettings,and unbonded webs) is sometimes preferred. Variations of one or severalof these steps allows for the enormous range of nonwoven fiber types.The term "staple fibers" was originally applied to fibers of naturalorigin long enough to be processed on textile machinery, but excludingendless filaments, eg, silk. In the present context, as applied to PHAof the present invention, "staple fibers" are of relatively uniformlength, ca. 1.3-10.2 cm, with a regular crimp i.e., a three-dimensionalwavelike shape. Regenerated and other extruded fibers are endless asformed. They are cut during the manufacturing process to a specifiedlength to meet a processing or market need. Extruded fibers are alsoproduced as continuous filaments without crimp. The processes forforming webs from staple fibers are different from those usingcontinuous filaments. The products obtained from staple and filamentfiber webs may differ substantially in properties (see EPSE-2).

The mechanical properties of the fibers as defined by their chemicalcomposition, determine the ultimate properties of the fabric. Webstructure and bonding maximize inherent fiber characteristics (seeEPSE-2). Other materials that may be used in the nonwovens of thepresent invention in combination with the PHA are wood pulp; regeneratedfibers including viscose rayon and cellulose acetate; and syntheticfibers like poly(ethylene terephthalate) (PET), nylon-6, nylon 6,6,polypropylene (PP), and poly(vinyl alcohol). Facings of disposablediapers or sanitary napkins made from PHA nonwoven fabrics of thepresent invention preferably feel dry even when the absorbent, innerabsorbent layer is saturated. Important fiber characteristics thataffect performance include length, diameter, density, crimp, crosssection shape, spin-finish (lubricant that is added to the surface ofextruded fibers to enhance processability), delustering (small amountsof TiO₂ pigment added before extrusion to increase whiteness or toreduce sheen) and the draw ratio.

a. Web-making methods

The characteristics of the fiber web determine the physical propertiesof the final product. These characteristics depend largely on fiberarchitecture, which is determined by the mode of web formation. Fiberarchitecture includes the predominant fiber direction, whether orientedor random, fiber shape (straight, hooked, or curled), the extent ofinterfiber engagement or entanglement, crimp, and compaction(web-density control). Web characteristics are also influenced by fiberdiameter, length, web weight, and chemical and mechanical properties ofthe polymer (see EPSE-2).

The choice of method for forming the web is determined by fiber length.Initially, the methods for forming webs from staple-length fibers(fibers long enough to be handled by conventional spinning equipment,usually from about 1.2 to about 20 cm long, but not endless) are basedon the textile-carding process, whereas web formation from short fibersis based on papermaking technologies. Although these technologies arestill in use, other methods have been subsequently developed. Forexample, webs are formed from long, virtually endless filaments directlyfrom bulk polymer; both web and fibers are produced simultaneously (seeEPSE-2). A variety of web-making methods are known, including carding,air-laying, wet-forming, spinbonding, and meltblowing.

The carding process is derived from the ancient manual methods of fibercarding, where natural staple fibers were manipulated by beds ofneedles. In carding, clumps of staple fibers are separated mechanicallyinto individual fibers and formed into a coherent web by the mechanicalaction of moving beds of closely spaced needles.

In the air-laying process, the orientation created by carding iseffectively improved by capturing fibers on a screen from an airstream(see U.S. Pat. No. 3,338,992, G. A. Kinney, assigned to E. I. du Pont deNemours & Co., Inc., issued Aug. 29, 1967). The fibers are separated byteeth or needles and introduced into an airstream. Total randomizationwould exclude any preferential orientation when the fibers are collectedon the screen.

Wet-forming processes employ very short fibers. Initially, webs areformed from short fibers by modified papermaking techniques. The fibersare continuously dispersed in a large volume of water and caught on amoving endless wire screen. Once the web is caught on the screen, it istransferred to belts or felts and dried on heated drums (see EPSE-2).

The spunbonded web process involves making fibers and websimultaneously, directly from bulk polymer. The bulk polymer is melted,extruded, and drawn (often by triboelectric forces) to filaments thatare randomized and deposited onto belts as a continuous web. Thefilaments are virtually endless. The spunbond process produces webs oflow crimp filaments in the normal diameter range of about 1.7 dtex (1.5den) or slightly higher. The birefringence and uniformity of diameter ofthese filaments are similar to standard textile fibers and filaments(see EPSE-2). Each production line is suitable for a specific polymerand a single-bonding system (see U.S. Pat. No. 4,163,305 (Aug. 7, 1979),V. Semjonow and J. Foedrowitz (to Hoechst AG)).

Webs are also made directly from bulk polymers by the meltblown process(see U.S. Pat. No. 3,322,607, S. L. Jung, assigned to E. I. duPont deNemours & Co., Inc., May 30, 1967). The molten PHA is forced throughvery fine holes in a special die into a high velocity airstream wherethe PHA is formed into very fine, although irregular, filaments ofindeterminate lengths. The filaments are simultaneously formed into aweb where melting and resolidification, and possibly static forces, holdthem together (see EPSE-2). The web consists primarily of filaments withvery fine diameters.

b. Web bonding

The bonding of fibers gives the strength to the web and influences otherproperties. Both adhesive and mechanical means are used. Mechanicalbonding employs the engagement of fibers by frictional forces. Bondingcan also be achieved by chemical reaction, i.e., formation of covalentbonds between binder and fibers (see EPSE-2).

D. Melt Temperature

Preferably, the biodegradable PHAs of the present invention have a melttemperature (Tm) of from about 30° C. to about 160° C., more preferablyfrom about 60° C. to about 140° C., more preferably still from about 90°C. to about 120° C.

E. Absorbent Articles

The present invention further relates to absorbent articles comprising aPHA of the present invention. Such absorbent articles include, but arenot limited to, infant diapers, adult incontinent briefs and pads, andfeminine hygiene pads and liners. Films of the present invention used asliquid impervious backsheets in absorbent articles of the presentinvention, such as disposable diapers, typically have a thickness offrom 0.01 mm to about 0.2 mm, preferably from 0.012 mm to about 0.051mm.

In general, the liquid impervious backsheet is combined with a liquidpervious topsheet and an absorbent core positioned between the topsheetand the backsheet. Optionally, elastic members and tape tab fastenerscan be included. While the topsheet, the backsheet, the absorbent coreand elastic members may be assembled in a variety of well knownconfigurations, a preferred diaper configuration is described generallyin U.S. Pat. No. 3,860,003, entitled "Contractible Side Portion forDisposable Diaper" which issued to Kenneth B. Buell on Jan. 14, 1975.

The topsheet is preferably, soft-feeling, and non-irritating to thewearers skin. Further, the topsheet is liquid pervious, permittingliquids to readily penetrate through its thickness. A suitable topsheetmay be manufactured from a wide range of materials such as porous foams,reticulated foams, apertured plastic films, natural fibers (e.g., woodor cotton fibers), synthetic fibers (e.g., polyester or polypropylenefibers) or from a combination of natural and synthetic fibers.Preferably, the topsheet is made of a hydrophobic material to isolatethe wearer's skin from liquids in the absorbent core.

A particularly preferred topsheet comprises staple-length fibers havinga denier of about 1.5. As used herein, the term "staple-length fibers"refers to those fibers having a length of at least about 16 mm.

There are a number of manufacturing techniques which may be used tomanufacture the topsheet. For example, the topsheet may be woven,nonwoven, spunbonded, carded, or the like. A preferred topsheet iscarded, and thermally bonded by means well known to those skilled in thefabrics art. Preferably, the topsheet has a weight from about 18 toabout 25 g/m², a minimum dried tensile strength of at least about 400g/cm in the machine direction, and a wet tensile strength of at leastabout 55 g/cm in the cross-machine direction.

The topsheet and the backsheet are joined together in any suitablemanner. As used herein, the term "joined" encompasses configurationswhereby the topsheet is directly joined to the backsheet by affixing thetopsheet directly to the backsheet, and configurations whereby thetopsheet is indirectly joined to the backsheet by affixing the topsheetto intermediate members which in turn are affixed to the backsheet. In apreferred embodiment, the topsheet and the backsheet are affixeddirectly to each other in the diaper periphery by attachment means suchas an adhesive or any other attachment means known in the art. Forexample, a uniform, continuous layer of adhesive,. a patterned layer ofadhesive, or an array of separate lines or spots of adhesive may be usedto affix the topsheet to the backsheet.

Tape tab fasteners are typically applied to the back waistband region ofthe diaper to provide a fastening means for holding the diaper on thewearer. The tape tab fasteners can be any of those well known in theart, such as the fastening tape disclosed in U.S. Pat. No. 3,848,594issued to Kenneth B. Buell on Nov. 19, 1974. These tape tab fasteners orother diaper fastening means are typically applied near the corners ofthe diaper.

Preferred diapers have elastic members disposed adjacent the peripheryof the diaper, preferably along each longitudinal edge so that theelastic members tend to draw and hold the diaper against the legs of thewearer. The elastic members are secured to the diaper in an contractiblecondition so that in a normally unrestrained configuration the elasticmembers effectively contract or gather the diaper. The elastic memberscan be secured in an contractible condition in at least two ways. Forexample, the elastic members may be stretched and secured while thediaper is in an uncontracted condition. Alternatively, the diaper may becontracted, for example, by pleating, an elastic member secured andconnected to the diaper while the elastic members are in their relaxedor unstretched condition.

The elastic members may take a multitude of configurations. For example,the width of the elastic members may be varied from about 0.25 mm toabout 25 mm or more; the elastic members may comprise a single strand ofelastic material or the elastic members may be rectangular orcurvilinear. Still further, the elastic members may be affixed to thediaper in any of several ways which are known in the art For example theelastic members may be ultrasonically bonded, heat and pressure sealedinto the diaper using a variety of bonding patterns, or the elasticmembers may simply be glued to the diaper.

The absorbent core of the diaper is positioned between the topsheet andbacksheet. The absorbent core may be manufactured in a wide variety ofsizes and shapes (e.g., rectangular, hour-glass, asymmetrical, etc.) andfrom a wide variety of materials. The total absorbent capacity of theabsorbent core should, however, be compatible with the designed liquidloading for the intended use of the absorbent article or diaper.Further, the size and absorbent capacity of the absorbent core may varyto accommodate wearers ranging from infants through adults.

A preferred embodiment of the diaper has an hourglass shaped absorbentcore. The absorbent core is preferably an absorbent member comprising aweb or batt of airfelt, wood pulp fibers, and/or a particulate absorbentpolymeric composition disposed therein.

Other examples of absorbent articles according to the present inventionare sanitary napkins designed to receive and contain vaginal dischargessuch as menses. Disposable sanitary napkins are designed to be heldadjacent to the human body through the agency of a garment, such as anundergarment or a panty or by a specially designed belt. Examples of thekinds of sanitary napkins to which the present invention is readilyadapted are shown in U.S. Pat. No. 4,687,478, entitled "Shaped SanitaryNapkin With Flaps" which issued to Kees J. Van Tilburg on Aug. 18, 1987,and in U.S. Pat. No. 4,589,876, entitled "Sanitary Napkin" which issuedto Kees J. Van Tilburg on May 20, 1986. It will be apparent that thefilms of the present invention comprising a PHA of the present inventiondescribed herein may be used as the liquid impervious backsheet of suchsanitary napkins. On the other hand it will be understood the presentinvention is not limited to any specific sanitary napkin configurationor structure.

In general, sanitary napkins comprise a liquid impervious backsheet, aliquid pervious topsheet, and an absorbent core placed between thebacksheet and the topsheet. The backsheet comprises a PHA of the presentinvention. The topsheet may comprise any of the topsheet materialsdiscussed with respect to diapers.

Importantly, the absorbent articles according to the present inventionare biodegradable and/or compostable to a greater extent thanconventional absorbent articles which employ materials such as apolyolefin (e.g., a polyethylene backsheet).

F. Synthesis of Biodegradable PHAs

The biodegradable PHAs of the present invention can be synthesized bysynthetic chemical or biological based methods. A chemical approachinvolves the ring-opening polymerization of β-lactone monomers asdescribed below. The catalysts or initiators used can be a variety ofmaterials such as aluminoxanes, distannoxanes, or alkoxy-zinc and-aluminum compounds (see Agostini, D. E., J. B. Lando, and J. R.Shelton, POLYM. SCI. PART A-1, Vol. 9, pp. 2775-2787 (1971); Gross, R.A., Y. Zhang, G. Konrad, and R. W. Lenz, MACROMOLECULES, Vol. 21, pp.2657-2668 (1988); and Dubois, P., I. Barakat, R. Jerome, and P. Teyssie,MACROMOLECULES, Vol. 26, pp. 4407-4412 (1993); Le Borgne, A. and N.Spassky, POLYMER, Vol. 30, pp. 2312-2319 (1989); Tanahashi, N., and Y.Doi, MACROMOLECULES, Vol. 24, pp. 5732-5733 (1991); Hori, Y., M. Suzuki,Y. Takahashi, A. Ymaguchi, and T. Nishishita, MACROMOLECULES, Vol. 26,pp. 4388-4390 (1993); and Kemnitzer, J. E., S. P. McCarthy, and R. A.Gross, MACROMOLECULES, Vol. 26, pp. 1221-1229 (1993)). The production ofisotactic polymer can be accomplished by polymerization of anenantiomerically pure monomer and a non-racemizing initiator, witheither retention or inversion of configuration of the stereocenter, orby polymerization of racemic monomer with an initiator whichpreferentially polymerizes one enantiomer. For example: ##STR8##

The naturally derived PHAs of the present invention are isotactic andhave the R absolute configuration at the stereocenters in the polymerbackbone. Alternatively, isotactic polymers may be made where theconfiguration of the stereocenters is predominantly S. Both isotacticmaterials will have the same physical properties and most of the samechemical reactivities except when a stereospecific reagent, such as anenzyme, is involved. Atactic polymers, polymers with randomincorporation of R and S stereocenters, can be produced from racemicmonomers and polymerization initiators or catalysts that show nopreference for either enantiomer while such initiators or catalystsoften polymerize monomers of high optical purity to isotactic polymer(e.g., distannoxane catalysts) (see Hori, Y., M. Suzuki, Y. Takahashi,A. Yamaguchi, T. Nishishita, MACROMOLECULES, Vol. 26, pp. 5533-5534(1993)). Alternatively, isotactic polymer can be produced from racemicmonomers if the polymerization catalyst has an enhanced reactivity forone enantiomer over the other. Depending on the degree of preference,separate R or S stereo-homopolymers, stereo-block copolymers, or amixture of stereo-block copolymers and stereo-homopolymers may beproduced (see Le Borgne, A. and N. Spassky, N., POLYMER, Vol. 30, pp.2312-2319 (1989); Tanahashi, N., and Y. Doi, MACROMOLECULES, Vol. 24,pp. 5732-5733 (1991); and Benvenuti, M. and R. W. Lenz, J. POLYM. SCI.:PART A: POLYM. CHEM., Vol. 29, pp. 793-805 (1991)). Some initiators orcatalysts are known to produce predominantly syndiotactic polymer,polymers with alternating R and S stereocenter repeat units, fromracemic monomer (see Kemnitzer, J. E., S. P. McCarthy and R. A. Gross,MACROMOLECULES, Vol. 26, pp. 1221-1229 (1993)) while some initiators orcatalysts may produce all three types of stereopolymers (see Hocking, P.J. and R. H. Marchessault, POLYM. BULL., Vol. 30, pp. 163-170 (1993)).

For example, preparation ofpoly(3-hydroxybutyrate-co-3-hexanoate-co-3-hydroxyalkanoate) copolymerswherein the 3-hydroxyalkanoate comonomer is a 3-alkyl-β-propiolactonewherein the alkyl group is at least 3 carbons long, are carried out inthe following manner. Proper precautions are made to exclude air andmoisture. The lactone monomers (purified, dried, and stored under inertatmosphere), β-butyrolactone and a 3-alkyl-β-propiolactone in thedesired molar ratio, are charged via syringe or canula to an oven-dried,argon-purged, and flamed borosilicate-glass tube or flask capped with arubber septum. The polymerization catalyst is added as a toluenesolution via syringe. The tube is carefully swirled to mix the reagents(but not contact the rubber septum) and then heated in an oil bath atthe desired temperature for the prescribed time. As the reactionproceeds the mixture becomes viscous and may solidify. If isotacticpolymer is produced, solid polymer precipitates out until the entiremass solidifies. The product can then be cooled, removed from the tube,and rid of residual monomer by vacuum drying. Alternatively, the productcan be dissolved in an appropriate solvent (e.g., chloroform) andrecovered by precipitation in a nonsolvent (e.g., ether-hexane mixture,3:1 v/v), and vacuum dried. Molecular weight is determined by standardmethods such as size exclusion chromatography (SEC, also known as gelpermeation chromatography or GPC). The comonomer content of the polymersis determined by nuclear magnetic resonance (NMR).

In a preferred method of synthesizing the PHAs of the present invention,the initiator is an alkylzinc alkoxide, as disclosed in the U.S. patentapplication entitled "Polymerization ofBeta-Substituted-Beta-Propiolactones Initiated by Alkylzinc Alkoxides",L. A. Schechtman and J. J. Kemper, assigned to The Procter and GambleCompany, filed Jan. 28, 1994. Such initiators have the general formulaR¹ ZnOR², wherein R¹ and R² are independently a C₁ -C₁₀ alkyl. In apreferred method of synthesis, the initiator is selected from the groupconsisting of ethylzinc isopropoxide, methylzinc isopropoxide, ethylzinc ethoxide, or ethylzinc methoxide; more preferably ethylzincisopropoxide.

Other copolymers useful in the present invention can be made bysubstituting the starting materials (monomers) in the above procedurewith 3-alkyl-β-lactones corresponding to the monomer units desired inthe final copolymer product.

Alternatively, biological synthesis of the biodegradable PHAs useful inthe present invention may be carried out by fermentation with the properorganism (natural or genetically engineered) with the proper feedstock(single or multicomponent). The production ofpoly(3-hydroxyalkanoate-co-3-hydroxybutyrate) by Aeromonas caviae isdisclosed in European Patent Application No. 533 144, Shiotani andKobayashi, published Mar. 24, 1993. Biological synthesis may also becarried out with botanical species genetically engineered to express thecopolymers of interest (see World Patent Application No. 93-02187,Somerville, Poirier and Dennis, published Feb. 4, 1993; and U.S. patentapplication Ser. No. 08/108,193, Somerville, Nawrath and Poirier, filedAug. 17, 1993; and Poole, R., SCIENCE, Vol. 245, pp. 1187-1189 (1989)).

G. EXAMPLES Example 1 Poly(3-hydroxybutyrate-co-hydroxyhexanoate)

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-Hx) is preparedaccording to the general methods described above and based on thepublished procedure of Hori et al. (Hori, Y., M. Suzuki, Y. Takahashi,A. Yomaguchi, and T. Nishishita, MACROMOLECULES, Vol. 26, pp. 5533-5534(1993)) for the polymerization of p-butyrolactone. Specifically,purified [S]-3-methylpropiolactone ([S]-β-butyrolactone) (9.50 g, 110mmol) and [S]-3-propylpropiolactone (0.66 g, 5.8 mmol) are charged intoa septum sealed, argon purged, dry, glass tube via syringe. Theinitiator, 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane preparedaccording to R. Okawara and M. Wada, (J. ORGANOMET. CHEM. (1963), Vol.1, pp. 81-88) and dried overnight in vacuo at 80° C. is dissolved in drytoluene to make a 0.18 M solution. Via syringe, 0.65 mL of the initiatorsolution (0.12 mmol distannoxane) is added to the tube. The tube isgently swirled to mix the contents and then heated at 100° C. for 4 h byimmersing its lower half in an oil bath. As the reaction proceeds, thecontents of the tube become viscous. After the required time, the tubeis removed from the oil bath and allowed to cool to room temperature.The solid is dissolved in chloroform. It is recovered by precipitationinto a hexane-ether mixture, collected by filtration, and dried undervacuum. The comonomer composition of the copolymer is determined by ¹H-NMR spectroscopy and found, within experimental error, to be the sameas the charge ratio (95:5). Molecular weight is determined by sizeexclusion chromatography with chloroform as the mobile phase, and narrowpolystyrene standards are used for calibration.

Example 2Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyoctanoate)

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyoctan-oate) isprepared by following the same procedure as in Example 1, with theexception that [S]-3-methylpropiolactone (9.50 9, 110 mmol),[S]-3-propylpropiolactone (0.40 g, 3.5 mmol) and[S]-3-pentylpropiolactone (0.50 g, 3.5 mmol) are used as the monomercharge.

Example 3Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxydecanoate)

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxydecanoate) isprepared by following the same procedure as in Example 1, with theexception that [S]-3-methylpropiolactone (9.50 g, 110 mmol),[S]-3-propylpropiolactone (0.40 g, 3.5 mmol) and[S]-3-heptylpropiolactone (0.60 g, 3.5 mmol) are used as the monomercharge.

Example 4Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyheptanoate)

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyheptanoate) isprepared by following the same procedure as in Example 1, with theexception that [S]-3-methylpropiolactone (9.50 g, 110 mmol),[S]-3-propylpropiolactone (0.40 g, 3.5 mmol) and[S]-3-butylpropiolactone (0.45 g, 3.5 mmol) are used as the monomercharge.

Example 5 Compostable Single Layer Film

PHB-Hx of composition 8 mole % hexanoate/92 mole % butyrate isintroduced into a single screw extruder (Rheomix Model 202) with screwdiameter of 0.75 inch. A constant taper screw having 20:1 length todiameter ratio and a 3:1 compression ratio is employed. The temperatureof both heating zones of the extruder barrel is 25° C. above the melttemperature of the PHB-Hx. The extruder is equipped with a die of width6 inch and a die gap of 0.04 inch. The die is maintained at 20° C. abovethe melt temperature of the PHB-Hx. The copolymer is melted within theextruder and pumped to the die at the other end of the extruder. Thescrew rpm is kept constant at 30 rpm. The copolymer is forced throughthe die and is collected on a take-up roll collection system (Postex) ata rate that allows crystallization of the copolymer before take-up. Thewidth of these films are nominally 4 inch and the thickness areapproximately 0.002 inch.

Example 6 Compostable Single Layer Film

Films of PHB-Hx are made by melting the material between Teflon sheetsin a Carver Press (Fred S. Carver Inc., Menomonee Falls, Wis.) at 20° C.above the melt temperature. Pressure on the sheets are adjusted toproduce films of approximately 0.25 mm thick. The films are thenidentically cooled to room temperature by placing the molds betweenlarge (5 kg) aluminum plates and allowing the films to cool to roomtemperature.

Example 7 Compostable Multilayer Film

Sheets of PHB-Hx film may be prepared as in Example 6. These sheets maythen encase a sheet of a polymer with good oxygen barrier properties buta poor water vapor transmission rate, or a polymer film that may bewater soluble such a poly(vinyl alcohol) (PVA). The films are placed incarver press stacked in the following order PHB-Hx(95:5), PHB-Hx(50:50),PVA, PHB-Hx(50:50), PHB-Hx(95:5). The material is then pressed at atemperature 5° C. above the melt temperature of PHB-Hx(50:50), but stillbelow the melting temperature of the PHB-Hx(95:5). After compression at2000 lb for 30 min, the pressure is released and the film is allowed tocool to room temperature.

Example 8 Comopostable Disposable Diaper

A disposable baby diaper according to this invention is prepared asfollows. The dimensions listed are for a diaper intended for use with achild in the 6-10 kilogram size range. These dimensions can be modifiedproportionately for different size children, or for adult incontinencebriefs, according to standard practice.

1. Backsheet: 0.020-0.038 mm film consisting of a PHB-Hx copolymer(prepared as described in Example 6); width at top and bottom 33 cm;notched inwardly on both sides to a width-at-center of 28.5 cm; length50.2 cm.

2. Topsheet: carded and thermally bonded staple-length polypropylenefibers (Hercules type 151 polypropylene); width at top and bottom 33 cm;notched inwardly on both sides to a width-at-center of 28.5 cm; length50.2 cm.

3. Absorbent core: comprises 28.6 g of cellulose wood pulp and 4.9 g ofabsorbent gelling material particles (commercial polyacrylate fromNippon Shokubai); 8.4 mm thick, calendered; width at top and bottom 28.6cm; notched inwardly at both sides to a width-at-center of 10.2 cm;length 44.5 cm.

4. Elastic leg bands: four individual rubber strips (2 per side); width4.77 mm; length 370 mm; thickness 0.178 mm (all the foregoing dimensionsbeing in the relaxed state).

The diaper is prepared in standard fashion by positioning the corematerial covered with the topsheet on the backsheet and gluing.

The elastic bands (designated "inner" and "outer", corresponding to thebands closest to, and farthest from, the core, respectively) arestretched to ca. 50.2 cm and positioned between the topsheet/backsheetalong each longitudinal side (2 bands per side) of the core. The innerbands along each side are positioned ca. 55 mm from the narrowest widthof the core (measured from the inner edge of the elastic bank). Thisprovides a spacing element along each side of the diaper comprising theflexible topsheet/backsheet material between the inner elastic and thecurved edge of the core. The inner bands are glued down along theirlength in the stretched state. The outer bands are positioned ca. 13 mmfrom the inner bands, and are glued down along their length in thestretched state. The topsheet/backsheet assembly is flexible, and theglued-down bands contract to elasticize the sides of the diaper.

Example 9 Compostable Lightweight Pantiliner

A lightweight pantiliner suitable for use between menstrual periodscomprises a pad (surface area 117 cm² ; SSK air felt 3.0 g) containing1.0 g of absorbent gelling material particles (commercial polyacrylate;Nippon Shokubai); said pad being interposed between a porous formed-filmtopsheet according to U.S. Pat. No. 4,463,045 and a backsheet whichcomprises a 0.03 mm thickness PHB-Hx copolymer film, as prepared inaccordance with Example 1.

Example 10 Compostable Sanitary Napkin

A catamenial product in the form of a sanitary napkin having two flapsextending outward from its absorbent core is prepared using a pad in themanner of Example 9 (surface area 117 cm² ; 8.5 g SSK air felt), per thedesign of U.S. Pat. 4,687,478, Van Tillburg, Aug. 18, 1987. Thebacksheet and topsheet materials are the same as described in Example 6.

Example 11 Compostable Disposable Diaper

The diaper of Example 9 is modified by replacing the backsheet with abacksheet consisting of a 0.020 to 0.038 mm thickness film comprising aPHB-Hx copolymer film (prepared as described in Example 6).

Example 12 Compostable Fiber

PHB-Hx of composition 5 mole % hexanoate/95 mole % butyrate isintroduced into a single screw extruder (Rheomix Model 202) with screwdiameter of 0.75 inch. A constant taper screw having 20:1 length todiameter ratio and a 3:1 compression ratio is employed. The temperatureof both heating zones of the extruder barrel is 25° C. above the melttemperature of the PHB-Hx. The extruder is equipped with a nozzle diecontaining 5 orifices of diameter 500 mm. The die is maintained at 20°C. above the melt temperature of the PHB-Hx. The polymer is meltedwithin the extruder and pumped to the die at the other end of theextruder. The screw rpm is kept constant at 30 rpm. The polymer isforced through the die and the melted extruded fibers are lead through aregion where a rapid air stream is applied such that the polymer fiberselongates and thins to approximately one fifth of the diameter of theorifices (ca. 100 mm). The fibers are collected on a cardboard mat. Awide distribution of fiber lengths are obtained up several cm in length.Most fiber lengths (over 50%) are in the range of 1.3 to 15 cm.

Example 13 Compostable Nonwoven Fabric

PHB-Hx of composition 4 mole % hexanoate/96 mole % butyrate isintroduced into a single screw extruder (Rheomix Model 202, Paramus,N.J.) with screw diameter of 0.75 inch. A constant taper screw having20:1 length to diameter ratio and a 3:1 compression ratio is employed.The temperature of both heating zones of the extruder barrel is 25° C.above the melt temperature of the PHB-Hx. The extruder is equipped witha nozzle die containing 5 orifices of diameter 500 mm. The die ismaintained at 20° C. above the melt temperature of the PHB-Hx. Thepolymer is melted within the extruder and pumped to the die at the otherend of the extruder. The screw rpm is kept constant at 30 rpm. Thepolymer is forced through the die and the melted extruded fibers arelead through a region where a rapid air stream is applied such that thepolymer fibers elongates and thins to approximately one fifth of thediameter of the orifices (ca. 100 mm). The fibers are collected on acardboard mat. The mat is moved in a fashion so that a 10 cm×10 cm areais covered uniformly with fibers. Collection of fibers on the matcontinues, until there is approximately 0.5 cm thick fiber mat. A widedistribution of fiber lengths are obtained up several inches in length.Most fiber lengths (over 50%) are in the range of 0.5 to 6 inches. Themat is then transferred to a Carver Press (Fred S. Carver Inc.,Menomonee Falls, Wis.) and pressed at a 1000 lb force for 10 minutes attemperature 5° C. below the melting temperature of the PHB-Hx. Theresulting nonwoven sheet is removed from the press.

All publications mentioned hereinabove are hereby incorporated in theirentirety by reference.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to one skilled in the art and are tobe included in the spirit and purview of this application and scope ofthe appended claims.

What is claimed is:
 1. An absorbent article comprising:a) a topsheet; b)a nonwoven backsheet comprising a biodegradable copolymer, wherein thebiodegradable copolymer comprises at least two randomly repeatingmonomer units wherein the first randomly repeating monomer unit has thestructure ##STR9## the second monomer unit has the structure ##STR10##and wherein at least 50% of the random repeating monomer units have thestructure of the first randomly repeating monomer unit, and wherein saidbiodegradable copolymer has a melt temperature of from about 30° C. toabout 160° C.; and c) an absorbent core positioned between the topsheetand the backsheet.
 2. The absorbent article of claim 1 wherein thebiodegradable copolymer comprises one or more additional randomlyrepeating monomer units having the structure ##STR11## wherein R¹ is H,or a C₂ or C₄ -C₁₉ alkyl or alkenyl; and n is 1 or
 2. 3. The absorbentarticle of claim 2, wherein R¹ is a C₂ or C₄ -C₁₉ alkyl.
 4. Theabsorbent article of claim 1, in the form of a disposable diaper,sanitary napkin, or pantiliner.
 5. The absorbent article of claim 1wherein the top sheet comprises a biodegradable copolymer, wherein thebiodegradable copolymer comprises at least two randomly repeatingmonomer units wherein the first randomly repeating monomer unit has thestructure ##STR12## the second monomer unit has the structure ##STR13##and wherein at least 50% of the random repeating monomer units have thestructure of the first randomly repeating monomer unit, and wherein saidbiodegradable copolymer has a melt temperature of from about 30° C. toabout 160° C.
 6. The absorbent article of claim 1 wherein the absorbentcore comprises fibers comprising a biodegradable copolymer, wherein thebiodegradable copolymer comprises at least two randomly repeatingmonomer units wherein the first randomly repeating monomer unit has thestructure ##STR14## the second monomer unit has the structure ##STR15##and wherein at least 50% of the random repeating monomer units have thestructure of the first randomly repeating monomer unit, and wherein saidbiodegradable copolymer has a melt temperature of from about 30° C. toabout 160° C.
 7. An absorbent article comprising:a) a topsheetcomprising a biodegradable copolymer, wherein the biodegradablecopolymer comprises at least two randomly repeating monomer unitswherein the first randomly repeating monomer unit has the structure##STR16## the second monomer unit has the structure ##STR17## andwherein at least 50% of the random repeating monomer units have thestructure of the first randomly repeating monomer unit, and wherein saidbiodegradable copolymer has a melt temperature of from about 30° C. toabout 160° C.; and b) a backsheet; and c) an absorbent core positionedbetween the topsheet and the backsheet.
 8. The absorbent article ofclaim 7 wherein the biodegradable copolymer comprises one or moreadditional randomly repeating monomer units having the structure##STR18## wherein R¹ is H, or a C₂ or C₄ -C₁₉ alkyl or alkenyl; and n is1 or
 2. 9. The absorbent article of claim 8, wherein R¹ is a C₂ or C₄-C₁₉ alkyl.
 10. The absorbent article of claim 7, in the form of adisposable diaper, sanitary napkin, or pantiliner.
 11. An absorbentarticle comprising:a) a topsheet; b) a backsheet; and c) an absorbentcore positioned between the topsheet and the backsheet, the absorbentcore comprising fibers comprising a biodegradable copolymer, wherein thebiodegradable copolymer comprises at least two randomly repeatingmonomer units wherein the first randomly repeating monomer unit has thestructure ##STR19## the second monomer unit has the structure ##STR20##and wherein at least 50% of the random repeating monomer units have thestructure of the first randomly repeating monomer unit, and wherein saidbiodegradable copolymer has a melt temperature of from about 30° C. toabout 160° C.
 12. The absorbent article of claim 11 wherein thebiodegradable copolymer comprises one or more additional randomlyrepeating monomer units having the structure ##STR21## wherein R¹ is H,or a C₂ or C₄ -C₁₉ alkyl or alkenyl; and n is 1 or
 2. 13. The absorbentarticle of claim 12, wherein R¹ is a C₂ or C₄ -C₁₉ alkyl.
 14. Theabsorbent article of claim 11, in the form of a disposable diaper,sanitary napkin, or pantiliner.